1. Field of the Invention
The present invention relates to a label feed control system for a label printer which issues a label after data from the weighing unit has been printed on the label sticked on the paper base ribbon.
2. Description of the Prior Art
An example of the conventional label feed control system will be described with reference to FIGS. 1 through 4. On a paper base ribbon 1 there are lightly adhered labels 2 of a certain size in a constant interval, and such ribbon 1 is wound on a label supply reel 3. The ribbon 1 is transported through a printer 4, a separator 5 on which a label is peeled off the base ribbon, and a feed roller 7 driven by a motor 6 to a ribbon take-up reel 8. On the upstream side of the printer 4 there is provided a photoelectric label position detector 9, and a label detector 10 which detects a peeled-off label 2 is provided at the front edge of the separator 5.
The weighing unit 11, the printer 4 and a keyboard 12 are connected to a CPU 13, which is further connected to an I/O port 14. The label detector 10 is connected through a label detection amplifier 15 to the I/O port 14. Also connected to the I/O port 14 is a feed controller 16, which is further connected to the motor 6 and to the position detector 9 through a position detection amplifier 18 having a variable resistor 17.
The label detector 10 produces a high D-signal when a label 2 is absent, and when an operation command, i.e. an A-signal, is issued with the signal D being high, the feed controller 16 produces a high C-signal to activate the motor 6 so that the ribbon 1 is fed. The signal C is also delivered to the CPU 13 via the I/O port 14 so as to interlock other operations during transportation. As the result of transporting the ribbon 1, a label 2 is peeled off the ribbon 1, projecting over the label detector 10 to cause its output signal D to become low. When the position detector 9 detects the label position and produces a B-signal, as will be described shortly, with the signal D being low, the signal C from the feed controller 16 turns low to stop the motor 6 and also to release the inhibited commands in the CPU 13.
The position detector 9 operates by sensing the transmissivity of the base ribbon 1 and the label 2. There are three cases in the amount of transmissivity as shown in FIG. 2-b: (a) a base ribbon 1 alone, (b) a label 2 on the base ribbon 1 and (c) a label with printed portion 20 on the base ribbon 1. The signal B is produced at the position where the base ribbon 1 alone exists. This system is based on the detection of the difference of light transmitted through the base ribbon 1 alone and the overlap of the base ribbon 1 and the label 2, and has the following problems. A label 2 having a high light transmissivity results in a very small transmission difference, requiring disadvantageously a very high accuracy of sensing. If the label 2 has a printed portion 20 as mentioned above for the shop name and the like, the lower transmissivity of this portion creates a large contrast relative to remaining portions of the label, resulting possibly in a failure of detection. Moreover, it is irksome to adjust the sensing level by the variable resistor 17 each time the thickness of the base ribbon 1 changes. In addition, the position detector 9 needs to be repositioned for each label size, and since the signal B from the position sensor 9 also serves as the operational reference for the printer 4, several labels are wasted for test printing in determination of the best setup position.
It is, therefore, the first object of the present invention to achieve the reliable positioning of the label irrespective of the right transmissivity of the label and the base ribbon.
The second object of the invention is to utilize the power frequency in positioning the label.
The third object of the invention is to control the label position digitally by use of a stepping motor.
The fourth object of the invention is to achieve the positioning of the label by numerical control.
The fifth object of the invention is to achieve the positioning of the label using the pulse signals generated by a slit disk.
The sixth object of the invention is to make common use of the detector for detecting the front edge of the label also for detecting the presence of the label, thereby controlling the print operation.
The seventh object of the invention is to achieve a sequential printing in the direction of label transportation, whereby print control and label feed control are performed reliably.
The eighth object of the invention is to achieve a sequential printing in the direction of label transportation in a simple label feed control.